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Figure 28

This figure shows four examples of rotational symmetry.

A hexagonal shape shows a mirror plane passing through the centre of each of the six faces and each of the six corners.

All 12 mirror planes intersect at a six-fold axis point at the centre of the hexagon.

A square shape shows a mirror plane passing through the centre of each of the four faces and each of the four corners.

All eight mirror planes intersect at a four-fold axis at the centre of the square.

A triangular shape shows a mirror plane passing through the centre of each of the three faces and each of the three corners.

All six mirror planes intersect at a three-fold axis at the centre of the triangle.

A parallelogram, with two unequal pairs of parallel sides, has no mirror planes and only a two-fold axis at its centre.

 6.1 Crystal symmetry